(1) Field of the Invention
The present invention relates to aluminum nitride bodies and an apparatus for producing semiconductors using such aluminum nitride bodies as substrates. The invention also relates to aluminum nitride sintered bodies and the production process thereof as well as to an apparatus for producing semiconductors using such aluminum nitride sintered bodies as substrates.
(2) Related Art Statement
In semiconductor-producing apparatuses such as etching apparatuses or chemical gas phase growing apparatuses, so-called stainless heaters or indirect-heating type heaters have been generally used. However, if such heat sources are employed, particles may be produced by the action of a halogen-based corrosive gas and a heat efficiency is poor. In order to solve those problems, NGK Insulators disclosed a ceramic heater in which a wire made of a high melting point metal is buried inside a dense ceramic substrate (JP-A 3-261131). This wire is sprailly coiled inside the discoidal substrate, and terminals are connected to the opposite ends of the wire. It has been discovered that such a ceramic heater has excellent characteristics suitable particularly for use in the production of semiconductors.
It is considered that nitride-based ceramics such as silicon nitride, aluminum nitride, and sialon are preferred as ceramics constituting substrates for the ceramic heaters. Further, a susceptor is sometimes placed on the ceramic heater, and a semiconductor wafter placed on the susceptor is heated. NGK Insulators, Ltd. disclosed that aluminum nitride is preferred as substrates for such ceramic heaters and susceptors (JP-A 5-101871). Particularly in the semiconductor-producing apparatuses, halogen-based corrosive gases such as ClF.sub.3 gas are often used as an etching gas or a cleaning gas. The reason why aluminum nitride is preferred is based on confirmation that aluminum nitride has extremely high corrosion resistance against such halogen-based corrosive gases.
An aluminum nitride sintered body itself generally exhibits white or whitish gray. However, it is desired that the substrate to be used as the abovementioned heater or susceptor is black, because the black substrate has a greater radiation heat capacity and a better heating characteristic as compared with the white ones. Further, if the white or gray substrate is used in the above heater or the susceptor, uneven color is unfavorably likely to appear at the surface thereof. Therefore, some improvement has been demanded. Further, customers prefer blackish brown, or blackish gray substrates and the like having a high black degree and a low lightness than the whitish or gray substrates.
In order to make an aluminum nitride sintered body black, it is known that an appropriate elementary metal or a metal compound (a blacking agent) is added into a powdery raw material, and a black aluminum nitride sintered body is produced by firing the resulting mixture (JP-B 5-64697). Such an additive, tungsten, titanium oxide, nickel, vanadium, etc. are known.
However, if an elementary metal or a metallic compound is incorporated into an aluminum nitride sintered body as a blacking agent, the content of metallic impurities in the aluminum nitride sintered body naturally becomes larger due to the incorporation of the additive. Particularly, if a Ia group element, a I element and/or a transition metal element exists in the aluminum nitride sintered body in the semiconductor-producing process, such element(s) adversely afford serious problem upon the semiconductor wafer or the semiconductor-producing apparatus, even if the content thereof is very small. For example, this may cause a defect in the semiconductor. Therefore, it has been demanded to decrease the lightness of the aluminum nitride sintered body without incorporating the above blacking agent therein.